A large-scale cyclonic-static microbubble flotation column (FCSMC) was tested at the Xuehu coal preparation plant for processing of fine particles (
0.5 mm). A measure of the axial gas holdup profile provided reasons for the deteriorating performance of the FCSMC. The results showed that an excessive mass flow rate of the solids resulted in the loss of mineralized bubbles to the tailings stream, which was responsible for the drop in the combustible recovery and tailings ash. This phenomenon gives rise to the gas holdup profile inversion where the increase of gas holdup from bottom to top decreases. It was shown that the critical tailings velocity of gas holdup profile inversion is exactly the same with the inflection point of carrying capacity and combustible recovery, which demonstrates that it is feasible to diagnose the column operation through the measurement of the axial gas holdup profile.